Liquid crystal display devices are widely used in the optical data processing field. The conventional liquid display modes include twister nematic, STN, in-plane switching, vertical alignment, multi-domain vertical alignment (MVA), OCB and the like. All of these modes cause the liquid crystal molecular orientation already under control to change into a different state of orientation when electrical fields are applied and change the polarization direction and polarization state of the transmitted light. The changes are converted into light and dark contrasts in polarized boards and the like to generally form a display.
These conventional liquid crystal display modes all require a surface orientation treatment in order to control the liquid crystal molecular orientation. A rubbing treatment is needed with the particular exception of multi-domain vertical alignment (MVA). The rubbing treatment is an operation in which a cloth or the like is used to rub an alignment film that has been surface coated onto a substrate surface and is in contact with liquid crystals, and is the cause of increased costs associated with fine dust and fine electric discharge which occurs due to high voltage static electricity.
The dusts cause a problem in highly fine pixel electrodes and thin-film transistors forming process in which film deposition, exposure, etching are repeated. The local electric discharge would damage the alignment film, or cause disconnection or electrostatic discharge damage in thin-film transistors and transparent electrode such as ITO. The existence of fine dust particles or fine electric discharge will result in declining yields and poorer display qualities. In addition, all of the modes described above use nematic liquid crystals, and their response times are about several milliseconds at the shortest, thus limiting their application in dynamic picture displays used for television.
To resolve the problems, the co-inventors have developed a chiral nematic liquid crystals for use in liquid crystal display devices. The development of a polymer-stabilized blue phase liquid crystal composite of the present invention to be used in place of the conventional nematic liquid crystals in order to solve the problems described above. A polymer-stabilized blue phase liquid crystal composite of the present invention is optically isotropic when no electrical field is applied, and the orientation does not need to be controlled.
The co-inventors have also developed a liquid crystal configuration using the novel blue phase liquid crystal composite in a novel mode involving no double refraction in the absence of an electrical field and a phenomenon that induces double refraction under applied electrical fields. The response time is about one hundred microseconds and is much faster than that of conventional liquid crystal display devices. However, a relatively low clearing point temperature limits application potential of currently existing polymer-stabilized blue phase liquid crystal composites, because the thermal effect from backlight could heat up the liquid crystal to its isotropic state so that the device cannot respond to the electric field.
Currently known polymer stabilized blue phase liquid crystal composites is that they require a relatively high voltage in order to achieve maximum transmittance in a voltage-ON state.
Simultaneously, an in-plane switching (IPS) mode was developed in response to the demand for larger liquid crystal screens and better quality displays. An electric field is applied on an equilibrium surface in a substrate in this mode, and a liquid crystal composite compatible with this mode is being sought. Application of such liquid crystal composite in TFT based display requires low threshold and operating voltages.